The Light Divide: 365 Days of Daylight in Stockholm vs Kolkata

I’ve lived in two cities that could not be more different in how they relate to the sun.

Kolkata — where I grew up — sits at 22.6°N. The sun rises reliably, sets reliably, and the day length stays in a narrow band between 10.5 and 13.5 hours year-round. Light is not something you think about in Kolkata. It just is.

Stockholm — where I live now — sits at 59.3°N. Here, light is a conversation topic, a mood regulator, a calendar. In June you can read a book at 10pm without a lamp. In December, the sun barely clears the horizon and sets at 2:47pm. The difference between the longest and shortest day is 13 hours — a full working day.

That contrast used to catch me off guard. Now I find it beautiful. And I wanted to visualize it properly.

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The Chart

The polar area chart below shows daily daylight hours for both cities across all 365 days of the year. Angle represents the day of year (clockwise from January 1 at the top), and radius represents hours of daylight. Hover any point to see the exact date and hours for both cities.

Interactive · Hover to explore

The Light Divide

Daily daylight hours across 365 days — Stockholm vs Kolkata

Stockholm59.3°N

Kolkata22.6°N

Stockholm peak

18h 37m

Jun 21

Stockholm low

6h 04m

Dec 21

Kolkata peak

13h 31m

Jun 21

Kolkata low

10h 45m

Dec 21

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What the Shape Tells You

Stockholm’s ring is dramatic. The inner depression in winter and the outer spike in summer create a shape that almost looks like a comet — a tight dark core with a blazing northern tail. In June, Stockholm averages 18 hours 37 minutes of daylight. In December, just 5 hours 53 minutes. The difference is staggering.

Kolkata’s ring is almost a circle. That evenness is real — not boring. It means the rhythm of your day barely shifts across the year. Sunrise is always around 5–6am. Sunset is always around 5–6pm. The tropics give you a kind of temporal stability that high latitudes never will.

The crossover happens twice a year. Around the equinoxes (March 20 and September 22), both cities briefly converge at around 12 hours of daylight — the only moments in the year when the sun treats them equally.

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Why I Find This Fascinating

There’s a theory that the dramatic light cycle in Scandinavia shaped the culture here — the intense social withdrawal of winter (hygge, stillness, inwardness), the explosive outdoor energy of summer (midsommar, midnight runs, cafe tables that appear overnight). Stockholm summers feel almost frantic with people trying to extract every last minute from the light.

In Kolkata, the relationship with outdoor life is modulated more by heat than light. You avoid going out at 1pm in May not because there’s no sun, but because there’s too much of it.

Same planet. Completely different relationship with the star at the centre of our solar system.

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The Math

The day lengths are computed using the Forsythe formula — a compact astronomical approximation that takes latitude and day-of-year as inputs:

P = arcsin(0.39795 × cos(0.2163108 + 2 × atan(0.9671396 × tan(0.00860 × (day − 186)))))
arg = (sin(0.26667°) × sin(P) − sin(φ)) / (cos(φ) × cos(P))
dayLength = 24 − (24/π) × arccos(clamp(arg, −1, 1))

Where φ is the latitude in radians. This gives accuracy within a few minutes for most latitudes. The chart uses a pure React + SVG implementation — no D3 required.

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Living between two latitudes doesn’t just change your address. It changes your body clock, your mood calendar, your relationship with darkness. Seeing the data laid out like this makes that visceral — one city drawing a tight, even circle, the other reaching outward in summer like it’s grasping at the light before winter pulls it back.

The light divide is real. And it’s beautiful.